Building a 260 Mhz Yagi Antenna.

[JamesWest]

I want to build a Yagi like the one shown on:

https://uhf-satcom.com/satellite-reception/uhf

that is based on the NBS standard yagi. I am having trouble finding a description of a 50 ohm coax or connector being attached to the two elements. It is not a folded dipole which i like because it is much easier to construct. also i will be using it receive only. PVC boom. Aluminum tube elements. i may increase the number of directors.

 

[VK3RX]

At the feed point there would be a 1:1 50 Ohm balun.

That design is similar to my Yagi, except mine has phasing straps for additional driven elements to provide the 250-270MHz coverage.

If you haven't already, you might look at the omni directional UHF satcom antenna mentioned in the thread below. Further down the page are parts 1 and 2 of the MT article, and further info in the thread..

Quite simple construction and they work well.

MT magazine UHF Satcom antenna project

This months Monitoring Times magazine has the conclusion of a two part article on making an omni directional UHF satcom antenna. The first part was in the March issue. Is anyone making one of these? prcguy

forums.radioreference.com

 

[prcguy]

A conventional Yagi is not wide band enough to get the entire UHF satcom downlink band unless its got a folded dipole.

 

[JamesWest]

A conventional Yagi is not wide band enough to get the entire UHF satcom downlink band unless its got a folded dipole.

what frequency would you use as the "center" of the band?

 

[prcguy]

The satcom downlink band is roughly 245 to 270MHz so the middle is about 257MHz. Problem is a Yagi antenna performance drops off quickly above its design frequency so its hard to design one without lots of computer simulation. I have one here and it has a two element log periodic type driven element to achieve the band width.

what frequency would you use as the "center" of the band?

 

[vagrant]

Here is a sweep of an Elk Log Periodic. The model is 220L6. It is made for the 220 MHz amateur band. I am doubtful it compares with a Yagi, or your purpose built two element driven log, but just for info.

 

[prcguy]

Another thing with a Yagi is its linear polarized and the satellite downlink is Right Hand Circular Polarized. You will loose about 3dB gain pointing a single Yagi at the satellite. You really want a RHCP antenna with some gain. A single two element Yagi will have about 5dBi gain but subtract about 3dB giving you about 2dBi gain or about 0dBd gain. A two element cross pol Yagi with proper phasing between elements is about 5dBic gain, so you get to keep all the gain needed for the satellite downlink.

 

[JamesWest]

Another thing with a Yagi is its linear polarized and the satellite downlink is Right Hand Circular Polarized. You will loose about 3dB gain pointing a single Yagi at the satellite. You really want a RHCP antenna with some gain. A single two element Yagi will have about 5dBi gain but subtract about 3dB giving you about 2dBi gain or about 0dBd gain. A two element cross pol Yagi with proper phasing between elements is about 5dBic gain, so you get to keep all the gain needed for the satellite downlink.

OK thank you and everybody for your input. Very helpful. I am rethinking doing this myself and I have found someone who builds antennas locally. Here are some photos of his 2m 440 sat antennas. He says no problem with 257 mhz. Hard to tell from the photos but it looks like he know what he is doing. I am not sure how broadband these antennas will be and I have to run RHCP by him. also this person does not speak English so I will try to have a conversation about that with him.

My issue is I am in a SEA jungle and have very limited access to materials or ebay or anything a long those lines. that is why i started out simple. But like everything I do, it just becomes more complex and i have to have two antennas and then three towers and ten radios.